Devices such as a cellular phone, a digital camera, a PDA, a touch panel display, a large-screen television, and contact-less power transfer show a tendency of further prevalence.
A tempered glass, which is produced by applying tempering treatment to glass through ion exchange treatment or the like, is used for those applications (see Patent Literature 1 and Non Patent Literature 1).
In addition, in recent years, the tempered glass has been more and more frequently used in exterior parts of, for example, digital signage, mice, and smartphones.
Characteristics required of the tempered glass include (1) high mechanical strength, (2) low cost, and (3) high dimensional accuracy. In digital signage applications, a structure in which a plurality of panels are linked together has been adopted in an increasing number of cases, and in association with this, a higher level of dimensional accuracy has been demanded. Specifically, while a conventional dimensional tolerance has been about ±4,000 ppm, a demand has arisen for a dimensional tolerance of about ±1,000 ppm.